docs: def handleHeader(self, key, value):
          "extends handleHeader to save headers to a local response object"
          key_lower = key.lower()
          if key_lower == 'location':
              value = self.modLocationPort(value)
          self._response.headers[key_lower] = value
          if key_lower != 'cache-control':
              # This causes us to not pass on the 'cache-control' parameter
              # to the browser
              # TODO: we should have a means of giving the user the option to
              # configure how they want to manage browser-side cache control
              proxy.ProxyClient.handleHeader(self, key, value)